The present invention relates to a yarn false twist texturing machine used in the production of synthetic yarn. Such machines typically comprise a plurality of side-by-side processing points (also referred to as stations)--usually up to 216.
False twist texturing machines of said type comprise a plurality of processing points--usually up to 216 processing points--which are arranged adjacent to one another along the length of the machine. Each of said processing points comprises a first delivery mechanism and a second delivery mechanism. The first delivery mechanism withdraws the yarn from a supply bobbin and delivers it into a false twisting zone. The second delivery mechanism draws the yarn out of the false twisting zone and delivers it to a take-up device, the yarn speed and the stretching of the yarn being determined by the speed ratio between the second and first delivery mechanism.
When texturing synthetic yarns, yarn speeds are customary which demand both a suitably long heating zone and a suitably long cooling zone. In the false twisting process, the quality of the achieved crimping is influenced particularly by the yarn tensile force prevailing in the individual regions inside the false twisting zone. Thus, for example, it is known that a low yarn tensile force not yet jeopardizing the stable yarn course is required in the heating zone for achieving good crimping. On the other hand, it has also been observed that increasing the yarn tensile force, say, in the region of the cooling rail produces improved results. It would therefore be desirable to adjust a yarn tensile force in the false twisting zone which leads to good results both during the heat treatment and during cooling.
From EP 0 638 675 a false twist texturing machine is known which comprises a twist-stopping device in the form of a rotatable transport roller inside the false twisting zone.
Although this does achieve the effect that the friction force exerted by the twist-stopping device upon the yarn leads only to a slight variation of the yarn tensile force, the absolute value of the yarn tensile force in the false twisting zone is substantially dependent upon the draw ratio adjusted between the first and second delivery mechanisms. Thus, a variation of the yarn tensile force in the false twisting zone would be achievable only by varying the yarn speed.
An object of the invention is accordingly to provide possible ways of influencing or controlling the yarn tensile force prevailing in the false twisting zone substantially independently of the yarn speed.
A further object of the invention is to achieve a piecing facility which is particularly protective of the yarn, gentle yarn processing and hence higher texturing speeds. It is likewise an object of the invention to provide a false twist texturing machine, in which each processing point is easily controllable independently of the adjacent processing points.